This invention is concerned with operating controls for gas turbine power plants, and, more particularly, is concerned with the power output stabilization of gas turbine power plants. It is specifically concerned with an inlet-exhaust temperature differential responsive control, i.e., a shutdown control, for a gas turbine power plant.
The typical gas turbine power plant comprises a single unit which embodies the functions of a compressor, a combustion chamber, and a working turbine unit. The compressor and working turbine unit are mechanically coupled on a common shaft so that the working turbine rotates the compressor. The common working fluid, air at ambient temperature, is supplied by the surrounding atmosphere. This air is drawn into the compressor when the turbine is operating and is compressed therein to a moderate pressure. The compressor is driven as indicated above by a shaft common to the turbine unit.
The compressed air then passes into the combustion chamber. Fuel is continuously supplied to the combustion chamber and is continuously burned as the compressed air passes through. The compressed air is heated as combustion takes place and a steady stream of high gases is produced. These gases leave the combustion chamber and go into the working turbine unit. The working turbine unit receives the high temperature gases and expands them to convert the thermal energy into mechanical energy at the shaft. The power at the shaft above and beyond that needed to drive the compressor is the net output power of the gas turbine power plant. After the expansion, the hot gases are discharged into the atmosphere.
The power output of the gas turbine power plant is normally controlled by controlling the flow of fuel into the combustion chamber. The power output characteristics of the typical gas turbine power plant described above are in part determined and limited by the temperature differential between the air temperature at the air inlet and the exhaust gas temperature. The power output of a particular turbine is a function of the differential in temperature between the air inlet temperature and the exhaust gas temperature. This temperature differential is also a reflection of mechanical stresses which exist within the gas turbine power plant. The controls of the gas turbine power plant to limit power output and limit mechanical stresses may be designed to operate on measurements of this temperature differential. By constraining the gas turbine power plant to operate within prescribed temperature differential constraints, power output and the integrity of the power plant may be carefully controlled.
The turbine control circuitry based on the inlet-exhaust temperature differential must accurately measure this temperature differential and, furthermore, accurately compare the temperature differential to predetermined operating constraints of the gas turbine power plant. A suitable control system should monitor the temperature differential and respond thereto to control the fuel flow to the gas turbine power plant to maintain its desired operating constraints.
Gas turbine power plants typically do not always have identical temperature differential responsive operating characteristics at different absolute operating temperatures. For example, if the air entering a gas turbine power plant is too low in temperature, the power plant could easily generate power to an extent where it would damage itself mechanically even though the exhaust temperature is within safe limits. Therefore, any control circuit responsive to a temperature differential must establish operating constraints which are compatible with the desired response of the gas turbine power plant at different absolute operating temperatures.